Since the laser linewidth is an important performance-metric for devices that use laser light, determining the precise value of linewidth is an essential prerequisite for evaluating the overall performance of laser-based devices. However, due to the influence of various kinds of noises, current laser linewidth detection methods are unable to measure the laser linewidth accurately. Accordingly, we propose a simple laser linewidth detection method, which uses the coherent envelope power spectrum to characterize laser linewidth based on the short delay self-homodyne system. Relying on theoretical derivation, simulations, and experiments, the feasibility and accuracy of proposed method are verified. This new approach is expected to enable the realization of a compact and precise laser linewidth measurement method.